Electron multiplier



April 5, 1938. G. B. BANKS x w 2,113,264

ELECTRON MULT IPLIER FiledV Aug. 31, 1937 INVEN TOR. 50/265 mow/N BAA/Ksi ATTORNEY."

Patented Apr. 5, 1938 UNITED STATES 2,113,264 ELEoTaoN MULTIPLIER GeorgeBaldwin Banks, Chelmsfo'rd,*Ei`1gl`alnil-lfas-z signor to RadioCorporation'of America, a corn 4 poration of Delaware Application August..s1,.1937,seria1.No. 161,731

Y In Great Britain Junef26, 19361 4 claims. (ol. 25o-27.5)k

As :is known,` electron multiplication uponk this l principle may beeiected in. almost any desired l\.;.number ofstages, very largevamplification of an original :electron stream being thus possible.Electron multipliers oi the magnetic type as disc1osed,lfor example, invUnited StatesPatent 2,078,304,Zworykin et al., April 27, 1936, utilizelga row of secondary electron lemitter electrodes situated in .oneplane, a row of electrostatic field electrodes situated in a parallelplane,- a primary cathode at .one end and an output electrode near theotherv end of the. row of secondary emitters, ,and a magnetic eldA inthe space between the two rows of electrodes. Such devices, especiallywhen multi-stage, require rather high applied unidirectional operatingpotentials in order to obtain thenecessary potential'gradient betweenthe" quency alternating electrostatic eldsobtainedV through connectionssuch that alternate secondary emitters are connected in a group in whichall emitters are ofA one instantaneous polarity, the remaining secondaryemitters inv another group 4o in which all emitters are of the otherinstan taneous polarity, and the instantaneous polarity of each fieldelectrode is the same as that of the secondary emitter electrode whichis next the emitter directly opposite the field electrode in question.Preferably,

emitters of one group are connected together within the envelope to oneexternal connection lead, the remaining alternate electron emitters ofthe other group are connected together within the envelope to anotherexternal lead, and alternate eld electrodes are also connected withinthe envelope to form two groups ofconnectedvelec#-` trodes so that all-of the field electrodes in reach group are ofthe same instantaneouspotential :one another andas thecorresponding groupof the alternateelectron l is obtained much the-same mannerl .as in the' emitters; With'this-arrang'ementf -andfl if the'l device 'has sa fphot'oelectri'c, asdistinct j from thermionicfprimary-jcathode only thre'ef external gconnections :arev necessary,4 one` to fthe output electroda'and--theothers to `the two external =5" 1 terminals by. whi'ch the 'high"frequency alternating potential-isV applied. to the two cooperating*groupsv ofemitters", and?! ot fieldelectrodesi y One embodiment of'theinvention is shown l diagrammatically in the" accompanyingdraw'ing-,f10*" y which shows an electron; discharge devicehaving anlevacuated cylindrical or other suitablyshaped'f f bulb orenvelope'Bren'clo'sing an emitter ofvprimar'y electrons, Isuch asi aphotocatho'de E t,y aplural-v ranged sideby side-in` the same planewith'fon'eoanother to rforma rowof vseven electron emitters lwith'theprimaryemitterat one'- end, the output anodeBbeingmounted nearthe `otherend.l Thev sevenr' eld- I electrodes are'f' mounted sideby' 1side to-forin-a'row of eld electrodesina plane paralf 'o lelItoftheplanev'of the row ofemitters. Therst elcl.v electrode F`9`isf-opposite and- `faces the V primary'vcathode andre'ach of the otherfield'felec# trodes is` oppositeand facesa corresponding sec; ondary-femitter. v f -Y Thelirst field electrode Vandl the primary'oath` odefor-in a pair of kopposedlspaced electrodes, one

of which is an electron-emitter, land the otherA field electrodes andthesecondary emitters formk six-other'similar pairsof electrodes.` Thesepairs of electrodes mounted side by side form two rows of electrodes inparallel-planes- Any oddnumber" Ofsuch"pairs may be used, the drawingshowing seven"I pairs; whichl is a convenient number ofA` stages.- Theoutputanode is` a plate at rightlo i.:

angles-to vthe planes of v'the rows of emitters and field electrodes,and-is'situated atthevend remote `from the primary cathode, facingvtoward the space between vthe two planes.

A-magnetio field extending between and trans- 451,

verse tothe rows of electrodes ina planeparallel to the planesof theelectrodes is produced by" .a magnet' M which il may conveniently becon-l structed and mounted as shown in the above mentioned United StatesPatent 2,078,304.' 'f

Althoughthe tu'befisoperated with a rather low alternating potentialinstead of with the" l rather! highl unidirectional poten-tialgenerallyv usedffor'ele'ctron multipliers, the multiplication PATENToFFIfCE prior electron multipliers, as the electrons 'from the iirstemitter ow along a curved path to the second emitter where secondaryelectron multiplication occurs, the secondary electrons from the secondemitter flow along a curved path to the third emitter, where furthermultiplication takes place, and so on until the output electrode isreached. j .t

In accordance with the invention there is impressed on the rows ofemitters and eld elecm trodes an alternating potential high enough tocause the electrons to iiow from one emitter to the next and producemultiplication, and of a frequencysuch that the period of each halfcycle is substantially the same as the transit time of an electronmoving from one emitter to the next. In order to obtain the successivemultiplications with an alternating operating potenfield electrodes anda connector `or Wire L--I- joining the emitters and extending throughthe Wall-of the envelope to `an external terminal Tv-I The second,fourth, and sixth emitters, that is ;E-2, E-ll, and E-B, are connectedthrough wires W to the rst, third, and fifth electrodes F-9, F-I l,F-I3, and also to v.one another and to the seventh or last fieldelectrode F-IS by a wire or connection of negligible impedance L- 2,v

which extends through the Wall of the bulb to a second external terminalT-2. Eachvfield electrode, except the last one, is connected by a wire Wto the emitter next to that emitter which is opposite the fieldelectrode, so that field electrodes F-S to F-M are connected to emittersE--2 to Erl--l respectively. A source S of alternating voltage, of highfrequency for example from 50 to 100 megacycles, has its oppositepolesconnected to the external terminals T-I and T-Z. The output anode A isconnected to o ne of the terminals, through a load impedance O and abattery or similar source of potential D having its negative terminalgrounded.

The operation of the device is as follows:

When light falls` on the primary emitter or photocathode E-l primaryelectrons are emitted. On the iirst half cycle of the alternatingoperating voltage the rstreld electrode F--B andv the second emitterlil-2 become positive with respect to the primary cathode, and theprimary or photo-electrons travel in more or less curved paths toand-impinge on the second emitter E-2, causing secondary electronemission. The frequency and amplitude of the high frequency voltage waveapplied to the terminals T--I and T-2 arev so chosen that the transittime of the electrons from each emitter to the next is equal to one-halfcycle of the impressed voltage, consequently at the momentof impact ofthe primary electrons on the second emitter E-2 at the end of thepositive cycle, that emitter and the lirst field electrode F--B are justreversing in instantaneous polarity. During the next orI second halfcycle both the next or third emitter E--3 and the second fieldAelectrode F--IU become positive with respect to the second emitter E--2,so that secondary electrons emitted from` the second emitter lil-2 aredrawn away by the positive field electrode F-IU and move toward thenextor third emitter E-3 in approximately similar curved paths. On reversalin polarity during the third lhalf cycle the secondary electrons fromthe third emitter E-S similarly move to the fourth emitter E--4, and soon, along the length of the discharge device, until the outputanode isreached, the electron stream being Amultiplied `at each impact.

Although the potential of the second emitter -E--2` is zero at the timethe primary electrons the first action is one of minication becauseelectrons can leave the photocathode only during the half cycle when therst eld electrode and rst emitter are positive with respect to it.During' the otherV half cycle the electrons cannot leavev the cathode.As only those electrons which are emitted during the rst 607 of thefavorable half cycle will arrive at the first emitter under favorableconditions for multiplication, only a fraction of the primaryphotoelectrons leave the cathode underiavorable conditions, but all. ofthe electrons constituting this fraction will reach the first secondaryemitter at a moment and under conditions suitable for the emission ofsecondary electrons, and similarly, these secondary electrons will ndconditions favorable for multiplication during their passage through thedevice.

It is evident that with the above described arrangement there is no needfor any very high potential supply, as the oscillatory electrostaticfield may be of comparatively low amplitude, and furthermore, the numberof external connections is reduced to three only.

E claim:

l. An electron multiplier comprising an evacuated envelope enclosing arow of discrete electron emitters in one plane, a row of correspondingdiscrete `field electrodes mounted in a parallel plane and each oppositean emitter, an output anode adjacent the last emitter and the lastv eldelectrode in said rows, a connector of negligible-impedance inside saidenvelope between the, rst emitter and each alternate emitter in the-row,a second connector of negligible impedance inside the envelope betweenthe second emitter, each alternate emitter in the row, and the lastfield electrode, each of said connectors extending through the wall ofsaid envelope to form ank external terminal, and means inside saidenvelope conductively connecting each iield electrodeexcept the last tothe emitter next to and further vaway from the first emitter than theemitter opposite said eld electrode.

2. An electron multiplier comprising two rows of the same odd number ofdiscrete opposed electrodes mounted in spaced parallel planes, an anodeat one end of said rows of electrodes, two connections of negligibleimpedance inside said envelope and extending from all said electrodesthrough the ,Wall of the envelope to two external terminals, the`alternate electrodes in eachv row= as counted from the same end beingconnected by one of said connections to cause the odd number electrodesin the first row and the even number electrodes in the second row all tobe maintained at the same instantaneous potential and by the other ofsaid connections to cause the even number electrodes in the first rowand the odd number electrodes in the second row all to be maintained atthe same instantaneous potential.

3. An electron multiplier comprising an evacuated envelope enclosing anodd number of discrete electron emitters mounted in a ro-w in the sameplane, the rst emitter in the row being a primary electron emitter, anequal number of discrete field electrodes mounted in a row in a planeparallel to the plane of the row of emitters with each eld electrodeopposite an emitter, an output anode adjacent the last emitter and thelast eld electrode in said ro-Ws, one co-nnection of negligibleimpedance inside said envelope connecting and thereby maintaining at thesame instantaneous potential the first and each alternate emitter andthe second and each alternate eld electrode, said connection extendingthrough the Wall of said envelope to provide an external terminal, and asecond connection o-f negligible impedance inside said envelopeconnecting and thereby maintaining at the same instantaneous potentialthe second and each alternate emitter and the rst and each alternatefield electrode, said second connection extending through the wall ofthe envelope to provide a second external terminal.

4. An electron multiplier comprising an evacuated envelope enclosing anodd number of discrete pairs of spaced opposed electrodes mounted sideby side to form two rows of electrodes in parallel planes, one electrodeof each pair being an electron emitter and the other a field electrode,means for producing a magnetic eld between and transverse to said rowsand parallel to the planes of said rows, an output anode adjacent oneend of said rows of electrodes, a conductive connection including anexternal terminal connecting all of the even number emitters and all ofthe odd number field electrodes except the last, and a secondco-nnection including another external terminal connecting all of theodd number emitters and all of the even number field electrodes.

GEORGE BALDWIN BANKS.

